Production of amalgams



June 24, 1958 A. WURBS 2,840,520

PRODUCTION OF AMALGAMS Filed July 26, 1954 8 3 L f l fi A r 1 r INVENTOR.

HLFRED wumas wjm United States The present invention relates to improvements in the production of amalgams and more particularly to the production of amalgams by the electrolysis of metallic electrolytes utilizing mercury as the cathode in the electrolytic cell.

The production of amalgams, and more particularly of alkali metal amalgams, as the starting material for many chemical reactions has become of increasingly greater importance since the development of the method of producing such amalgams by the electrolytic decomposition of alkali chloride solutions and the like utilizing a moving mercury cathode.

The amalgams produced by this method and particularly the alkali amalgams such as sodium amalgam may be used for many purposes, such as for the production of the sodium metal, for the reaction of the amalgam with polysulfide to form sodium sulfide, in the production of alkali hydroxide and hydrogen by the reaction of the alkali metal amalgam with water, in the synthesis of sodium hydrosulfite or sulfoxalate by the reaction of sulfur dioxide with the sodium of the amalgam, in the reduction of organic substances such as nitrobenzene with the amalgam to form azobenzene or hydrazobenzene, etc. In general it is desirable to have the metal such as sodium in rather high concentration in the amalgam.

There are several reasons for the desirability of obtaining amalgams of higher concentration. For example, the velocity of the reaction with the amalgam is increased by the use of amalgams of higher concentration; the proportion of mercury which has to be distilled-off in the recovery of the sodium, relative to the amount of sodium recovered, is reduced; the proportion of impurities carried along by the amalgam is reduced. However, in those cases in which the optimum temperature for the reaction, of the alalgam does not correspond with the temperature of formation of the amalgam in the electrolytic cell, and this is generally the case, it becomes desirable to reduce the heat transportation between the two apparatuses which occurs by the circulation of mercury by arranging that for each unit of weight of sodium produced the smallest possible amount of mercury is utilized as carrier for the sodium. I

The importance of realizing this latter condition may be be appreciated for, example by the fact that in the reaction of sodium amalgams with water in a decomposer to form sodium hydroxide and hydrogen, a reaction which is favored by the highest possible temperature, about twothirds of the available reaction heat is carried oil to the cell due to the circulation of mercury when the sodium concentration in the amalgam is maintained at the usual level of -12 g./l.

By doubling this concentration of sodium in the amalgam it is possible with otherwise unchanged conditions and without the use of a heat exchanger to increase the temperature differential between the decomposer and the electrolytic cell for example from 16 C. to more than 30 C. a

In other cases however, for example in the production atent 2 of hydrosulfite, the reaction should take place under intensive cooling to the lowest possible temperature, about 10-25 C. At a temperature differential between the electrolytic cell and the reactor of, for example, 35 C. not less than 1300 calories per kg. of sodium are transferred from the cell to the hydrosulfite apparatus by the transportation of the amalgams if the amalgam concentration is at the usual level of 12 g./l. This large amount of heat is taken out of the electrolytic cell on the one hand and must be drawn-01f from the reactor on the other hand by artificial cooling means. Therefore, for reasons of economy, it is desirable to reduce this heat transfer as much as possible. If necessary,

, the reduction in heat transfer achieved by increasing the amalgam concentration can additionally be improved by a heat exchange between the amalgam feeding into the reactor and the amalgam leaving the reactor.

In any event, it may be seen that it is desirable in th electrolytical production of the amalgams to increase as much as possible the concentration of the metal, e. g. sodium, in the amalgam. This may be done without difliculties by repeated circulation of the amalgam in the electrolysis cell so as to gradually enrich the sodium content of the amalgam, and then to work up the thus obtained amalgam.

However, this method of proceeding is disadvantageous. it is' obviously much more desirable to work by means of a continuous process for the production of the amalgam by electrolysis and in the reaction of the produced amalgam.

If it is attempted to achieve the continuous process by somewhat slowing the mercury circulation in the conventional horizontal cells, it has been found that after only a few hours and at a sodium concentration of about 20 g./l. there is an increase in the hydrogen generation It is a further object of the present invention to provide a process whereby amalgam of high concentration may be continuously produced in an electrolytic cell and continuously reacting the formed amalgam in a reactor whereby the above-enumerated ditficulties in such continuous proceeding are avoided.

It is a furhter object of the present invention to provide a continuous method ofproducing amalgam of high concentration utilizing a circulating mercury cathode moving at a sufiiciently high speed toprevent undue hydrogen generation in the electrolytic cell and to remove salt incrustations from the fioor of the cell.

Other objects and advantages of the present invention will be apparent from a further reading of the specification and of the appended claims.

With the above objects in view, the present invention mainly consists in a process of electrolytically producing amalgams, comprising the steps of subjecting an electrolyte solution containing metal ions in solution to electrolysis utilizing a moving liquid mercury cathode in the electrolytic cell whereby the metal formed by electrolysisat the cathode is amalgamated with mercury, maintaining movementof said liquid mercury cathode in said electrolytic cell by continuously circulating part of the formed amalgam through the cell, and continuously withdrawing the remainder of the formed amalgam from the cell.

Thus, according to the method of the present invenwhen. r I

p a} Y tion, the amalgam isfcontinuously removed from the electrolytic cell and a portion only of the removed amalgam is reintroduced back into the electrolytic cell wherein it serves,,withthe addition of ,fresh mercury if necessary as .the cathode in the cell for the production of additional amalgam upon the electrolysis of the electrolyte solution. ..The rest of the removed amalgam, namely the am algam which is not reintroduced back into the electrolytic cell, may be collected or directly introducedinto a reactor for the reaction of the amalgam, e.. g. of sodium amalgam with water to form sodium hydroxide and hydrogen. Preferably, M144 of the amalgamis reintroduced back into the cell and the remainder led to the collecting vessel or reactor. Most preferably,,% of the removed amalgam is directly reintroduced baclg into the cell and the remainder, 95 -92, is led away to a collecting vessel or to a. reactor. The-,process-of the present invention is applicable to the formation pf amalgams of any metal .by theelcctrolysis of a solutionicontainingions of the particular metal in the presence of a mercury cathode. However, the present invention finds .-its most useful application in the production of alkali metal amalgamssuch as sodium amalgam potassium amalgam, lithium amalgam, etc., by the electrolysis of aqueous solutions of their soluble salts such as sodium chloride, potassium chloride, etc. At. the-start of the continuous. process of the present invention of forming the amalgam in the electrolytic cell and reacting the amalgam in areactor, by withdra ing the formed amalgam from the cell and reintroducing a portion of. the withdrawn amalgam, the amalgam concentration increases at first until eventually an equilibrium is set up between the amount of sodium reacted at any given time whichis equal to the amount formed.

It has also been found that the hydrogen generation which occursrwhen the speed of circulation of the mercury is decreased is notdue mainly to the higher concentrationof the. sodium in the amalgam. It has been found that, particularly in the case where unprotected iron is used for the floor of the cell, the amalgam has aten'dency to adhere to the floor. of the cell in the form of islands, or to form salt crusts, when the speed of circulationsof the mercury falls considerably below 80-100 liters .per dec'imeter of cell width and hour, and that these :floor incrustations are the cause of the increased generation of hydrogen. The present invention has the particular advantage of avoiding the formation of "such 'incrustations 'because the present invention allows .for theruseof the same or even higher circulation speedsof the mercury than is ordinarily found while still mercury which counteracts the tendency toward the for- I mation of deposits on the cell floor.

The process of thepresent invention therefore permits, in a technically simple and operationally safe manner, the formation of i alkali metal amalgams of very high concentration utilizing high circulation speeds of the mercury in the electrolytic cell by the expediency of reintroducing only a portion of the removed amalgam back into the electrolytic cell and feeding the remainder of the 'amalgam into an amalgam reaction apparatus. By varying the relationship between these two fractions, it is technically possible in a very simple manner to ad-v just. the proce'ssfor the production of amalgams of any desiredconc'entration.

lhis r'nethod is of coursemuch more simple and more practical thanflattempts to achieve the same result by the building of special ,cells 'of. abnormal length, or by greatly increasing the amount of mercury charged. into the cell. a.

The novel features which areconsidered as characteristic for the invention are set forth in particular in the appended claims.

4 The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing, in which the drawing diagrammatically illustrates an installation for carrying out the process of the present invention.

Referring more particularly to the drawing, the amalgam such as sodium amalgam which is formed in the electrolytic cell 1 by the electrolysis of the sodium chloride solution utilizing a mercury cathode is removed from the electrolytic cell 1 by the two conduits 2 and 3 or by a single conduit which could branch off into conduits 2 and 3. A predetermined portion of the amalgam, e. g. /t, removed from the cell 1 is introduced into the reactor 4 by conduit 2. The remaining portion of the amalgam is reintroduced into the cell 1 by means of conduit 3.

Additional fresh mcrcury to replace the removed amalgam may be introduced into the cell 1 from the supply source 5 by means of conduit 6. The mercury which is formed in the reactor 4 by the reaction of amalgam, e. g. with water, is carried by conduit 7 from the reactor. The mercury may at heat exchanger 10 be passed in heat exchange with the amalgam coming from the cell 1 through conduit 2 to the reactor 4. The mercury after heat exchange may then be carried by conduit 7 through con- Example The following are the characteristics of the cell in which the process takes place: 10,000 amperes, 8 kg. of sodium produced per hour, 800 liters of mercury per hour circulated.

with divided cirwlthout culation particidivided pating in rcaccirculation tion l./hr. through reactor..- 800 400 267 g./l.sodlu m: cell entrance 0 1D 20 g./l. sodium: cell exit"... 10 20 30 g./l. sodium: reactor run-ofi. 0 0 0 g./1. sodium: reacted 10 10 10 kgjhr. sodium: Na reacted 8 8 8 The process of the present invention therefore results in the possibility of achieving a high alkali metal content in the mercury circulating between the electrolytic cell and the amalgam reaction apparatus,and thereduction of the heat transfer caused by the mercury circulation between the electrolytic cell and the amalgam reactor.

Thus, by the present method utilizing for example a ratio of 1:1 between the amount of amalgam directly recirculated back into the electrolytic cell to the amount of amalgam conducted directly to the amalgam reactor, the concentration of alkali metal in the amalgam leaving the cell is double that which is achieved under otherwise similar conditions and, moreover, only half as much heat is exchanged between the electrolytic cell and the reactor by means of the circulating mercury as compared to that which would occur if all of the amalgam were removed from the electrolytic cell and led directly to the amalgam reactor.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. An electrolytic metal recovering method comprising, in combination, the steps of subjecting an electrolyte solution containing alkali metal ions to electrolysis in an electrolytic cell utilizing liquid mercury as cathode means, whereby the metal formed by electrolysis is amalgamated with said, mercury forming the amalgam of said metal; continuously removing the thus formed amalgam from said electrolytic cell; cooling a portion only of said removed amalgam; separating the mercury from said cooled portion of said removed amalgam so as to obtain said metal and free mercury; and continuously reintroducing said free mercury and the untreated remainder of said removed amalgam back into said electrolytic cell.

2. An electrolytic metal recovering method comprising, in combination, the steps of subjecting an electrolyte solution containing alkali metal ions to electrolysis in an electrolytic cell utilizing liquid mercury as cathode means, whereby the metal formed by' electrolysis is amalgamated with said mercury forming the amalgam of said metal; continuously removing the thus formed amalgam from said electrolytic cell; separating said continuously removed amalgam into first and second portions; separating the mercury from said first portions of said removed amalgam so as to obtain said metal and free mercury therefrom; passing said free mercury obtained from said first portions of said removed amalgam in heat exchange with subsequent first portions of said removed amalgam; and continuously reintroducing said free mercury obtained from said first portions of said removed amalgam and said untreated second portions of said removed amalgam back into said electrolytic cell.

3. An electrolytic metal recovering method comprising, in combination, the steps of subjecting an electrolyte solution containing alkali metal ions to electrolysis in an electrolytic cell utilizing liquid mercury as cathode means, whereby the metal formed by electrolysis is amalgamated with said mercury forming the amalgam of said metal; continuously removing the thus formed amalgam from said electrolytic cell; separating said continuously removed I amalgam into first and second portions; cooling said first portions of said removed amalgam; separating the mercury from said cooled first portions of said removed amalgam so as to obtain said metal and free mercury therefrom; passing said free mercury obtained fromsaid first portions of said removed amalgam in heat exchange with subsequent first portions of said removed amalgam; and continuously reintroducing said free mercury obtained from said first portions of said removed amalgam and said untreated second portions of said removed amalgam back into said electrolytic cell.

4. An electrolytic metal recovering method comprising, in combination, the steps of subjecting an electrolyte solution containing alkali metal ions to electrolysis in an electrolytic cell utilizing liquid mercury as cathode means, whereby the metal formed by electrolysis is amalgamated with said mercury forming the amalgam of said metal;

continuously removing the thus formed amalgam from said electrolytic cell; separating the mercury from of said removed amalgam so as to obtain said metal and free mercury; and continuously reintroducing said free mercury and the untreated remainder of said removed amalgam back into said electrolytic cell.

5. An electrolytic metal recovering method comprising, in combination, the steps of subjecting an electrolyte solution containing alkali metal ions to electrolysis in an electrolytic cell utilizing liquid mercury as cathode means, whereby the metal formed by electrolysis is amal gamated with said mercury forming the amalgam of said metal; continuously removing the thus formed amalgam from said electrolytic cell; separating the mercury from Va of said removed amalgam so as to obtain said metal and free mercury; and continuously reintroducing said free mercury and the untreated remainder of said removed amalgam back into said electrolytic cell.

6. An electrolytic metal recovering method comprising, in combination, the steps of subjecting an electrolyte solution containing alkali metal ions to electrolysis in an electrolytic cell utilizing liquid mercury as cathode means, whereby the metal formed by electrolysis is amalgamated with said mercury forming the amalgam of said metal; continuously removing the thus formed amalgam from said electrolytic cell; separating said continuously removed amalgam into first and second portions, said first portions constituting between A and of the entire continuously removed amalgam; cooling said first por: tions ,of said removed amalgam; separating the mercury from said cooled first portions of said removed amalgam so as to obtain said metal and free mercury therefrom; passing said free mercury obtained from said first portions of said'removed amalgam in heat exchange with subsequent first portions of said removed amalgam; and continuously reintroducing said free mercury obtained from said first portions of said removed amalgam and said untreated second portions of said removed amalgam back into said electrolytic cell.

7. An electrolytic metal recovering method comprising, in combination, the steps of subjecting an electrolyte solution containing alkali metal ions to electrolysis in an electrolytic cell utilizing liquid mercury as cathode means, whereby the metal formed by electrolysis is amalgamated with said mercury forming the amalgam of said metal; continuously removing the thus formed amalgam from said electrolytic cell; separating said continuously removed amalgam into first and second portions, said first portions constituting between /2 and of the entire continuously removed amalgam; cooling said first portions of said removed amalgam; separating the mercury from said cooled first portions of said removed amalgam so as to obtain said metal and free mercury therefrom; passing said free mercury obtained from said first portions of said removed amalgam in heat exchange with subsequent first portions of said removed amalgam; and continuously reintroducing said free mercury obtained from said first portions of said removed amalgam and said untreated second portions of said removed amalgam back into said electrolytic cell.

8. An electrolytic metal recovering method comprising, in combination, the steps of subjecting an electrolyte solution containing alkali metal ions to electrolysis in an electrolytic cell utilizing liquid mercury as cathode means, whereby the alkali metal formed by electrolysis is amalgamated with said mercury forming the amalgam of said alkali metal; continuously removing the thus formed amalgam from said electrolytic cell; separating the mercury from a portion only of said removed amalgam so as to obtain said alkali metal and free mercury; and continuously reintroducing said free mercury and the untreated remainder of said removed amalgam back into said electrolytic cell.

9. An electrolytic meta-l recovering method comprising, in combination, the steps of subjecting an electrolyte solution containing sodium ions to electrolysis in an electrolytic cell utilizing liquid mercury as cathode means, whereby the sodium formed by electrolysis is amalgamated with said mercury forming the amalgam of said sodium; continuously removing the thus formed amalgam from said electrolytic cell; separating the mercury from a portion only of said removed amalgam so as to obtain said sodium and free mercury; and continuously rein roducing said tree mercury and the untreated re- 7 main'der or i said removed amalgam back into said elec tr'olytic celli-f '10. An electrolytic metal recovering "methodwompris; ing, in -combination, the steps of subjecting {an 'electro lyte solution containing potassium ions to electrolysis in an electrolytic cell utilizing liquid mercury as cathode means, whereby the potassium formedfby electrolysis is amalgamated with said mercury forming "the amalgam of said potassium; continuously removing (the thus formed'amalgam "from said electrolyticbellfseparating the mercury from a portion only of said removed amalgam so as to obtain said potassiumand free mercury; and continuously reintroducing said free mercury and the untreated remainder of said removed amalgam back into said electrolytic cell.

11. An electrolytic metal recovering method comprising, in'combination, the steps of subjecting an aqueous sodium chloride solution to electrolysis in an electrolytic cell utilizing liquid mercury as cathode means, whereby the metal formed by electrolysis is amalgamated with'said mercury forming the amalgam of said metal; continuously removing the thus formed amalgam from said electrolytic cell; separating the mercury from a portion only of said removed amalgam'so as to'obtain said metal and free, mercury; and continuously reintroducing said free mercury and the untreated remainder of said 'removed amalgam back into said electrolytic cell.

12. An electrolytic 'metal recovering method comprising, in combination, the steps of subjecting an electrolyte solution containing alkali metalions to electrolysis in an electrolytic cell utilizing liquid mercury as cathode means, whereby the alkali metal formed by electrolysis is 'amalgamated with said mercuryforming the amalgam'of said alkali metal; continuously removingthe thus formed amalgam fromsaid electrolytic cell; separating said continuously removed amalgarn'into first and second portions; cooling said first portions of said removed amalgam; separating the mercury from said cooled first portions of said removed amalgam so as to obtain said alkali metal and free mercury therefrom; passing said free mercury obtained from saidfirst portions of said removed amalgam in heat exchange .With subsequent first portions of said removed amalgam; and continuously reintroducing said free mercury obtained 'from said first portions of said removed amalgam and said untreated second poris "amalgamated with saidmercury forming the amalgam of saidialkali metal; continuously removing the thus formed 'amalgamfifrom said electrolytic cell; separating the mercury from %%1 of said removed amalgam so as to obtain said alkali metal and free mercury; and continuously reintroducing said free mercury and the untreated "remainder of said removed amalgam back into said electrolytic cell.

14. An electrolytiometal recovering method .comprising, in combination, the steps of subjecting an electrolyte solution containing alkali metal ions to electrolysis in an electrolytic cell utilizing liquid mercury as cathode means, whereby thealkali metal formed by electrolysis is amalgamated with said mercury forming the amalgam of said metal; continuously removing the thus formed as .ngani "from said electrolytic cell; separating said continuously'removed amalgam into first and second portions, said first portions constituting between A and A of the entire continuously removed amalgam; cooling said first portions of said removed amalgam; separating the mercury from "said cooled first portions of said re-. moved amalgam so as to obtain said alkali metal and free mercury therefrom; passing said free mercury ob tained from said first portions of said removed amalgam in heat exchange with subsequent first portions of said removed amalgam; and continuously reintroducingsaid free mercury obtained from said first portions of said removed amalgam and said untreated second portions of said removed amalgam back into said electrolytic cell.

15. An electrolytic metal recovering method comprising, in combination, the steps of subjecting an electrolyte solution containing alkali metal ions to electrolysis in an electrolytic cell utilizing liquid mercury as cathode means, whereby the metal formed by electrolysis is amalgamated with said mercury forming the amalgam of said metal;

continuously removing the thus formed amalgam from said electrolytic cell; heating a portion only of said re moved amalgam; separating the mercury from said heated portion of said removed amalgam so as to obtain said metal and free mercury; and continuously reintroducing said free mercury and the untreated remainder of said removed amalgam back into said electrolytic cell.

References Cited in the file of this patent UNITED STATES PATENTS 2,234,967 Gilbert Mar. 18, 1941 2,351,383 Wolf June 13, 194-4 2,677,656 Overbeck May 4, 1954 2,748,072 Paoloni et a1. May 29 1956 2,750,281 Vanharen 'et al June 12, 1956 

1. AN ELECTROLYTIC METAL RECOVERING METHOD COMPRISING, IN COMBINATION, THE STEPS OF SUBJECTING AN ELECTROLYTE SOLUTION CONTAINING ALKALI METAL IONS TO ELECTROLYSIS IN AN ELECTROLYTIC CELL UTILIZING LIQUID MERCURY AS CATHODE MEANS, WHEREBY THE METAL FORMED BY ELECTROLYSIS IS AMALGAMATED WITH SAID MERCURY FORMING THE AMALGAM OF SAID METAL; CONTINUOUSLY REMOVING THE THUS FORMED AMALGAM FROM SAID ELECTROLYTIC CELL; COOLING A PORTION ONLY OF SAID REMOVED AMALGAM, SEPARATING THE MERCURY FROM SAID COOLED PORTION OF SAID REMOVED AMALGAM SO AS TO OBTAIN SAID METAL AND FREE MERCURY, AND CONTINUOUSLY REINTRODUCING SAID FREE MERCURY AND THE UNTREATED REMAINDER OF SAID REMOVED AMALGAM BACK INTO SAID ELECTROLYTIC CELL. 